Performance investigation and enhancement of membrane-contactor microchannel absorber towards compact absorption cooling

Abstract

Solar absorption cooling is a promising approach to address the energy and environmental issues. Large-size and low-efficiency are two big challenges for wider applications of solar absorption cooling, while membrane-based microchannel absorbers are potential for effective enhancement in compactness and efficiency. To investigate the local heat and mass transfer characteristics of membrane-based microchannel absorbers, a two-dimension coupling model is developed and validated. The influences of key parameters and entrance effect on the absorption rate are analyzed in detail. Results show that the average absorption rate increases by 40% as the solution channel thickness decreases from 1 mm to 0.15 mm, but the pressure drop in the solution channel increases nearly exponentially. Meanwhile, as solution inlet velocity increases from 0.002 m/s to 0.02 m/s, the average absorption rate increases by 56%. Considering both pressure drop and absorption rate, the recommended solution inlet velocity and channel thickness are approximately 0.004 m/s and 0.5 mm, respectively. In addition, an enhancement strategy (channel baffles) is proposed to improve the performance of microchannel absorbers. The average absorption rate of the baffled module increases to 0.0053 kg/(m2•s), which is 20% higher than that without baffles. As for the compactness, the volumetric cooling capacity with baffles is 230% higher than that of a conventional falling-film absorber. Given a similar volumetric cooling capacity, the pressure drop of the baffled absorber is approximately 50% lower as compared to the non-baffle absorber. This study can facilitate the in-depth analysis and optimal design of membrane-based microchannel absorbers towards compact solar absorption cooling systems.